FIG. 9 is a structural diagram showing a conventional LD excitation solid-state laser oscillator using an LD laser beam as an excitation light. Referring to FIG. 9, reference numeral 1 denotes a partial reflecting mirror that partially transmits a laser beam 8, and 2 is a total reflecting mirror which is opposed to the partial reflecting mirror 1 through a laser medium 3 and totally reflects the laser beam 8. Reference numeral 4 denotes a flow tube for cooling the laser medium 3 with water, and cooling water that cools the laser medium 3 flows in a gap between the flow tube 4 and the laser medium 3. Reference numeral 5 denotes a guide plate and transmits the excitation light radiated from an LD package 6 up to the laser medium 3. Reference numeral 7 denotes a reflector which shuts up the excitation light transmitted through the guide plate 5 therein and superimposedly reflects the excitation light within the reflector 7 to excite the laser medium 3.
FIG. 10 is a longitudinal cross-sectional view of an excitation section made up of the LD package 6 shown in FIG. 9 and shows the structure in which the laser medium 3 is excited. Reference numeral 6 denotes the LD package that emits the excitation light by allowing a current and cooling water to flow. Reference numeral 11 denotes a horizontal gap spacer and is set so that an LD bar (not shown) that emits the excitation light and the guide plate 5 that transmits the excitation light are located at a given distance. Reference numeral 12 denotes a vertical gap spacer which is set so that the excitation light enters the center of thickness of the guide plate 5. Reference numerals 13 and 14 denote a bolt and a nut for fixing the LD package 6, the horizontal gap spacer 11, the vertical gap spacer 12 and the reflector 7 together, respectively.
Subsequently, the operation will be given.
FIG. 9 is a structural diagram showing a general solid-state laser oscillator. In this example, the LD package 6 which is high in efficiency and compact is employed as the excitation section instead of the lamp. The excitation light outgoing from the LD package 6 (there are many cases in which a plurality of LD packages 6 are used in association with a laser output) passes through the guide plate 5 and excites the laser medium 3 through the flow tube 4 that constitutes a channel that cools the laser medium 3. The excitation light does not excite the laser medium 3 at once but excites the laser medium 3 by passing through the medium several times. For that reason, the reflector 7 is located around the laser medium 3 so as to efficiently take out the laser beam. A light quantum within the laser medium 3 is supplemented between the partial reflecting mirror 1 and the total reflecting mirror 2, and the laser beam 8 is emitted by a given excitation or more.
FIG. 10 also shows a method of guiding a light from the LD package 6 until the laser medium 3 is excited. The LD package 6 is formed of a diode and emits the excitation light from the LD bar by making a current flow from an LD package main body (not shown) to a sub-mount, the LD bar, a wire bonding and a cathode electrode (which are not shown). Also, in order to maintain the junction temperature of the LD bar at a given temperature or lower, cooling is conducted with cooling water. The excitation light passes through the guide plate 5 and excites the laser medium 3 through the flow tube 4 surrounded by the reflector 7 with a high efficiency. In this example, it is necessary to assemble the guide plate 5 and the LD bar of the excitation light outgoing section together with a given accuracy. For that reason, the horizontal spacer 11 is inserted so as to maintain a gap between the LD bar and the guide plate 5 at a given value, and the vertical spacer 12 is inserted so as to adjust the vertical position, to thereby enhance the light transmission efficiency.
On the other hand, as a light guide, there has been proposed a semiconductor laser device disclosed in Japanese Utility Model Unexamined Publication No. Sho 63-89273. FIGS. 11 and 12 show a structural diagram and a perspective view of a waveguide section used for detection of a laser beam according to an embodiment of that publication, respectively, and show a laser output stabilizing device which has been devised for optical pickup. Reference numeral 22 denotes a semiconductor laser that emits the light in both directions. Reference numeral 20 denotes a waveguide member having waveguide grooves 20-1, 20-2 and 20-3. Reference numeral 21 denotes a light receiving device having light receiving elements 21-1, 21-2 and 21-3. FIG. 12 is a birds-eye view of the waveguide member in which the respective LD lights are regulated by the waveguide grooves 20-1, 20-2 and 20-3 so as not to be interfered with each other and then guided lights up to the light receiving elements 21-1, 21-2 and 21-3.
The lights are for signal detection and emitted from the LD 22 in two directions, and one light is emitted to the light receiving device 21 and another light is used for reading, writing and erasing. The above LD 22 emitted in two directions is an LD of a multi-array (three functions in the figure). The stability of its output is very important for optical pickup, and the light is always detected by the light receiving device 21 to conduct output control. In order to make the waveguide member 20 compact, the array system is applied, and in order to surely separate the respective signals, the waveguide grooves 20-1, 20-2 and 20-3 are applied.
Incidentally, as shown in FIGS. 9 and 10, the structure using the guide plate 5 suffers from various problems, one of which is a cost problem. The guide plate 5 is very thin (0.3 to 0.7 mm) and upper and lower surfaces of the guide plate 5 must be subjected to micro-polishing for total reflection. Also, the outlet and inlet surfaces of the excitation light must be coated with an AR coat (coating for preventing reflection) after micro-polishing. The material of the guide plate 5 is high in refractive index, and a specific material low in absorption factor is required. In general, non-doped YAG or quartz is used which is very high in the costs.
Another problem is that assembling is difficult. The excitation light outgoing from the LD bar is about 1 micron, and the height of the LD package main body from a bottom surface thereof and the center of thickness of the guide plate 5 must be adjusted in height about several tens microns. Also, because a divergent angle is large, a gap between the outgoing surface of the LD bar and the guide plate 5 must be positioned in parallel, similarly, several tens microns. Because the height of the package main body of the LD bar from the lower surface thereof to a light emitting position varies, the horizontal spacer 11 and the vertical spacer 12 are actually selected so as to match its common difference and attached to the device. This maintains its transmission efficiency but the transmission efficiency is deteriorated if selection is in error.
Also, end surfaces of the guide plate 5 are subjected to the AR coating, resulting in such a problem that the coating is damaged by attachment of dusts and particles.
Further, still another problem is that three kinds of signals are separated by application of the waveguide grooves 20-1, 20-2 and 20-3 in Japanese Utility Model Unexamined Publication No. Sho 63-89273. In the case where light is guided to the waveguide grooves from the LD array 22, because the divergent angle of the LD array light is large, three lights cannot be sufficiently separated in this structure so as to be interfered with each other, and light is also leaked to the upper portion because of three walls, resulting in such a problem that the light transmission efficiency is deteriorated.
As described above, in the conventional device, because the guide plate 5 is used for LD light guide, there arise such problems that the costs are high, assembling is difficult, the transmission efficiency is deteriorated if adjustment is in error and a long-period reliability is low due to particles or the like. Also, there arises such problems that light separation cannot be sufficiently made because the waveguide grooves are applied but the light emitting section is located outside of the waveguide grooves, and the transmission efficiency is deteriorated because of three walls.
The present invention has been made in order to solve the above problems, and is to provide a semiconductor laser excitation solid-state laser device which conducts light transmission with a simple structure and a high efficiency and which is low in price, less varies in height, easy in assembling and high in reliability.